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Powering ESP Controller from dry contact connection

AMS7

New Member
Thread starter #1
Hi all.

So firstly I'm a complete noob when it comes to electronics so please excuse my shortcomings here.

My challenge. I have a dry contact connection that is outputting 12v. Ibwant to use this to power an ESP module (WemosD1). The challenge I have I assume is the current. When I connect the WEMOS to the power from the dry contact switch the voltage drops down to 1v. I've also tried to measure the amperage using a voltmeter and it seems it's outputting .01A (I think I'm reading it correctly).

So my question is, is it possible to power the module from this connection and if so how would I do it? What am I missing here, do I need to increase the current somehow? (I think the wemos requires about 150-250mA.

Thanks in advance
 

AMS7

New Member
Thread starter #3
It's a rj11 connection that would usually connect to a switch. I'm told it's a dry contact connection. - hope that clarifies?
 

AMS7

New Member
Thread starter #4
To help visualise. The power is coming from an AC motor used for a gate. And the RJ11 connection would have a reboundable switch connected to it to operate the motor direction.
 

AMS7

New Member
Thread starter #6
Lol. Okay so I have an AC motor used for an entry gate. This motor has an RJ11 connection on it which is supposedly used for a dry contact switch to operate it.

This RJ11 connection outputs 12v. So I want to use that connection to power the wemos.
 

Pommie

Well-Known Member
Most Helpful Member
#8
So, you have 4/6 connections? Two power, 12V and Gnd? Two that need shorting together to operate the gate? Any more?

This is like pulling hen's teeth.

Mike.
 

AMS7

New Member
Thread starter #9
Yeah sorry Mike but as I said I'm a noob.

I have 4 connections. 1 ground plus 12v plus two directional contacts. So if I short the 12v with either of the directional wires the motor turns in that direction.

Red - 12v
Black - Grnd
Blue - Direction 1
WHITE - Direction 2
 

Pommie

Well-Known Member
Most Helpful Member
#10
OK, we now know what connections you have but not what you want to achieve! If you just want to power the Wemos then a switch mode power supply should take 12V, 100 mA and power the Wemos without any problem.

Mike.
 
Thread starter #12
Thank you very for the information Mike

Can I assume that a switch mode PS is the same as a step down PS similar to the AMS1117? And by using this would/could it increase the current?

RE the WEMOS mini I'm also looking into this, thanks.
 

Pommie

Well-Known Member
Most Helpful Member
#13
A SMPS (switch mode power supply) is much more efficient so 12V 100mA in is 1.2W. This will probably give 1W out - 5V at 200mA. Might work - try it.

Mike..
 

JimB

Super Moderator
Most Helpful Member
#16
Like everyone else, I've no idea what a 'dry contact switch' means?
A common expression in the world of industrial controls is "Volt Free Contact", or sometimes "Volt and Earth Free Contact".
These expressions are used to describe a simple contact, either a switch or a relay contact, which is isolated from any electrical supply and earth.

The expression "Dry Circuit" is sometimes used where the voltage and current is so low that it cannot break through the oxide (?) layer on the surface of a relay contact.
An example of this was found in the amateur radio transceiver type FT102 by Yaesu.
In the RF circuits of the receiver section, there are many bandpass filters switched by relays.
These relays are switching signals at the microvolt level.
Over the years the contacts tarnish and the sensitivity of the receiver is severely impaired.
Part of the fix for this problem was to add resistors to give a "wetting current" to the contacts to prevent the problem recurring.

Coming back to the topic of the thread, the circuit described by the OP, sounds far from being a" dry contact".
It sounds like something which is intended to be connected to a Volt Free Contact.

JimB
 
Thread starter #17
@ Mike. From the UK - I'll try and source the same on eBay here. Thnx.

JimB. More than likely you're right it's not a dry contact but the motor was supplied from China and this is how they revered to it so I was using the same jargon. Thankfully I have experts like you guys to set me straight.. Thanks again all..
 

JonSea

Well-Known Member
Most Helpful Member
#18
Coming back to the topic of the thread, the circuit described by the OP, sounds far from being a" dry contact".
It sounds like something which is intended to be connected to a Volt Free Contact.

JimB
Exactly. In this case a simple switch or relay contact between +12v and either direction terminal controls which direction the gate moves.

Often, a dry contact input is connected to an optoisolator. In this case, the +12v signal is probably fed via a current-limiting resistor to provide a few mA to operate optoisolators connected to each direction terminal.

This current-limited output won't provide enough power to operate a WEMOS board.
 

Pommie

Well-Known Member
Most Helpful Member
#19
The OP said he got 100mA from the 12V supply. Is this unusual? I've not come across a system like this before.

Mike.
 

JonSea

Well-Known Member
Most Helpful Member
#20
No, he said he measured 0.01 amp = 10mA.

Also, it sounds like he set the meter to measure current and connected it between +12 and ground. Fortunately for the meter's sake, the +12 supply is current limited or the magic smoke would have been let out of the meter (or fuse if it had one) and maybe the power supply too.
 

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